How do I change the End Frame in an animation without changing the max frames in other animations within a character?
No.

The start frame and end frame are properties of the scene. That's is why they're located in the scene section of the properties area. Each scene has its own (but exactly one) start and end frame.

Actions have no start and end frame. They are automatically starting on their first keyframe and ending on their last keyframe. If you add an action to the NLA editor these are the frames which are used for the length of the action. (You can still trim the actions used frame range in the NLA editor.)